As illustrated in FIGS. 6 and 7, although a revolving frame 1 of a hydraulic shovel or the like has a skirt beam 3 which is fixed to a side surface of a center frame 2 by a welding portion 4, high stress is generated in an upper portion of the center frame 2 when a vehicle vibrates. Thus, on a rear side of a vehicle of which the height of the center frame 2 is low, a high stress generating portion 5 of the center frame 2 is close to the welding portion 4 of the skirt beam 3. As a result, the welding portion 4 is likely to be affected by the stress, and the strength and durability of the welding portion 4 are a matter of concern. Therefore, it is necessary to add a reinforcing material, processing of a weld toe, and the like during the welding.
On the other hand, a revolving frame in which a gap is formed between a center frame and a sponson beam for supporting a cab and the center frame and the sponson beam are not welded directly to prevent the influence of stress is proposed (for example, see Patent Document 1).